The present invention relates generally to electronic imaging apparatus incorporating a zoom lens, and more particularly to electronic imaging apparatus reduced in size, inclusive of video cameras and digital cameras.
In recent years, imaging apparatus such as digital cameras designed to take images of subjects using solid-state imaging devices such as CCDs or CMOSs have gone mainstream in place of silver-halide film cameras. Further, they have now a wide spectrum of categories from the commercial high-end type to the compact low-end type. The present invention gives weight to the compact low-end type category in particular.
Users of such low-end type digital cameras would enjoy snapping shots over a wide range of scenes at any time in any place. For this reason, preference is given to small-format digital cameras, especially of the type that can be well put away in the pockets of clothing or baggage, are convenient to carry around, and are slimmed down in their thickness direction, and there is a mounting demand for size reductions of taking lens systems, too. On the other hand, as the pixels of imaging devices are now on the increase, there is a mounting demand for higher optical performance keeping pace with a lot more pixels. Further, to make sure mass productivity, it is required to minimize the sensitivity of optical performance deterioration to production errors in the process of processing and assembling lenses. From the point of view of making taking ranges wide, high zooming lenses having zoom ratios exceeding 5 or 7, too, are generally available; much higher zoom ratios are expected, and so are wider-angle arrangements. To meet such demands, there are now various types of zoom lenses proposed in the art.
Among prior zoom lenses having relatively high zoom ratios and compact format, there is a type comprising, in order from its object side, a positive first lens group, a negative second lens group, a positive third lens group and a positive fourth lens group, as set forth in the following patent publication 1.
[Patent Publication 1]
JP(A)2006-171055
[Patent Publication 2]
JP(A)11-52244
[Patent Publication 3]
JP(A)8-271788
[Patent Publication 4]
JP(A)2003-241097
Problems with the zoom lens put forward in Patent Publication 1 are, however, that it is not fit for size reductions, because the lens system has a long full length. With the zoom lens set forth in Patent Publication 2 or 3, there is no sufficient optical performance ensured.
The above prior arts are all designed such that all over the zoom range, the angle of incidence of rays on the imaging device becomes small; any sensible tradeoff cannot be offered between good imaging capabilities and size reductions while making sure high zoom ratios.
The zoom lens proposed in Patent Publication 4 is supposed to be used with single-lens reflex cameras with silver halide films loaded inside; the back focus for making sure a mirror space is longer relative to the large angle of exit of rays from the zoom lens optical system. Such power profiles require a lot more lenses to obtain satisfactory imaging capabilities, making it difficult to achieve size reductions in the event that the zoom lens is used with a small-format imaging device.
The invention has been made to meet the users demands for making taking ranges wider than ever before without detrimental to the ability of cameras to be carried around: the invention has for its object the provision of electronic imaging apparatus using a less costly zoom lens optical system that satisfies the requirements of making cameras smaller and having high zoom ratios and wide-angle arrangements at the same time, enables the image quality of taken images to be well kept, and lends itself to imaging devices such as CCDs or CMOSs.